1. Field of the Invention
The present invention relates to a polarization illumination apparatus and a projector having the polarization illumination apparatus.
2. Related Background Art
FIG. 1 is a view showing an arrangement of main part of a conventional projector using a polarization illumination apparatus. The projector includes a light source 1, a reflection mirror 2, a polarization beam splitter 6, a polarization beam splitting film 20, a liquid crystal light valve 7, and a quarter-wave optical phase plate 13. In FIG. 1, the end portions of two polarization beam splitting films 20.sub.1 and 20.sub.2 are in contact with each other to form an angle of about 90.degree. therebetween. Random light Ao emitted from the light source 1 is converted into substantially parallel light (i.e., light substantially parallel to the optical axis) by the reflection mirror 2, and the parallel light is incident on the first polarization beam splitting film 20.sub.1. In this case, p-polarized light Ap.sub.1 is transmitted through the film 20.sub.1, and s-polarized light As is reflected by the film 20.sub.1. The S-polarized light As is further reflected by the second polarization beam splitting film 20.sub.2 arranged along the optical path, and is then converted into circularly polarized light Ar via the quarter-wave optical phase plate 13 whose optical axis is set in a desired direction. The circularly polarized light Ar is transmitted through the quarter-wave optical phase plate 13 again via the light source 1 and the reflection mirror 2, and is converted into light Ap.sub.2 including p-polarized light. The light Ap.sub.2 is transmitted through the polarization beam splitting film 20.sub.1, and is then incident on the liquid crystal light valve 7.
In this projector, the two polarized light components, i.e., the p-polarized light Ap and the s-polarized light split by the polarization beam splitting film 20.sub.1 or 20.sub.2 are converted to polarized light components having the same direction of polarization so as to illuminate the liquid crystal light valve 7. With this projector, light utilization efficiency can be improved as compared to a projector using no polarization illumination apparatus.
However, since the conventional projector uses the optical phase plate, the light amount is undesirably decreased due to absorption or reflection when light is transmitted through the plate. A conventional plastic optical phase plate has a light transmittance of about 90%. In particular, since a light beam, which returns to the light source 1, and then emerges therefrom, is transmitted through the optical phase plate a total of three times, the light amount is considerably decreased.